This invention relates to laser ophthalmic surgery and more particularly to a method and system particularly suited to panretinal photocoagulation procedures performed on a human patient.
Photocoagulation has been used for various ophthalmic procedures such as panretinal photocoagulation (PRP) and the like. Such procedures are performed using either a slit-lamp (SL) laser delivery system or, when surgical intervention is required, endo-ocular laser probes.
In the slit-lamp system, laser energy is delivered from the laser source to the imaging optics via a single optical fiber. As is known, the imaging optics are used in conjunction with a variety of contact lenses, and must be capable of focusing the output end (distal) of the fiber onto the retina The focal length of the imaging optics, is typically variable, i.e. zoom, to magnify the size of the fiber's image on the retina from 1 to 20 times, corresponding to 50-1000 microns on the retina.
Current SL systems offer a single fiber for single point exposure on the surgical area. The surgeon positions the fiber image to the desired location by observing a low energy aiming beam on the treatment area. By turning the laser on/off and moving the aiming beam, the surgeon can lay down a pattern of spots on the treatment area. The number of spots is determined by the size of the treatment area and the laser spot size desired. For photocoagulation of microaneurysms on the retina, the laser spot size must be small (&lt;100 microns) to avoid damage to surrounding tissue.
For medical conditions which require panretinal photocoagulation (PRP), also known as scatter photocoagulation, the area affected may include the entire retina outside the foveal region. The accepted mode of treatment is to lay down an uniform distribution of photocoagulative burns, with spot sizes of 250-500 microns and spaced at 1 times the spot diameter. A typical treatment consist of 1600 burns. The time to position the spot and deliver the laser energy depends on the features of the SL and the skill of the surgeon and is typically 2 seconds per spot. This means that the treatment time is in excess of 60 minutes which is fatiguing to the patient and surgeon. Also, laying down a uniform pattern is difficult and the pattern is typically more random than a geometric in distribution.
When PRP treatment requires surgical intervention, the SL is not used. Instead standard endoocular laser probes are employed. The treatment objectives are the same, however, to lay down a pattern of photocoagulative burns in the affected area. Using the endo-laser probe, the surgeon holds the distal tip close to the retina and lays down 1500-2000 spots, 500 microns in diameter. This procedure can take more than one hour. Using the probe close to the retina increases the risk of accidental tears and the length of the procedure prolongs the anesthesia time in high risk patient groups.